We aim to investigate the role of combination nivolumab, ipilimumab, and cabozantinib in rare histological variants of the GU tract, specifically: bladder/urachal adenocarcinoma, squamous cell carcinoma, and small cell carcinoma; variants of urothelial carcinoma including plasmacytoid, sarcomatoid, and others; renal tumors including sarcomatoid renal cell carcinoma and renal medullary carcinoma; and penile cancers. Tumor and blood samples will be collected on all rare GU tumor patients. We will obtain samples for immune subsets of circulating peripheral mononuclear blood cells, circulating tumor DNA (ctDNA) and use whole-exome sequencing to define the relationship between tumor mutational burden in each histologic subtype and response to drugs. We will also use RNA sequencing to define the relationship between expression-based subtypes, the immune contexture of the tumors and response to drugs.